/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina.filters;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Filter that attempts to force MS WebDAV clients connecting on port 80 to use
 * a WebDAV client that actually works. Other workarounds that might help
 * include:
 * <ul>
 * <li>Specifying the port, even if it is port 80, when trying to
 * connect.</li>
 * <li>Cancelling the first authentication dialog box and then trying to
 * reconnect.</li>
 * </ul>
 * <p>
 * Generally each different version of the MS client has a different set of
 * problems.
 * <p>
 * TODO: Update this filter to recognise specific MS clients and apply the
 * appropriate workarounds for that particular client
 * <p>
 * As a filter, this is configured in web.xml like any other Filter. You usually
 * want to map this filter to whatever your WebDAV servlet is mapped to.
 * <p>
 * In addition to the issues fixed by this Filter, the following issues have
 * also been observed that cannot be fixed by this filter. Where possible the
 * filter will add an message to the logs.
 * <p>
 * XP x64 SP2 (MiniRedir Version 3790)
 * <ul>
 * <li>Only connects to port 80</li>
 * <li>Unknown issue means it doesn't work</li>
 * </ul>
 */
public class WebdavFixFilter implements Filter {

	private static final String LOG_MESSAGE_PREAMBLE =
			"WebdavFixFilter: Detected client problem: ";

	/* Start string for all versions */
	private static final String UA_MINIDIR_START =
			"Microsoft-WebDAV-MiniRedir";
	/* XP 32-bit SP3 */
	private static final String UA_MINIDIR_5_1_2600 =
			"Microsoft-WebDAV-MiniRedir/5.1.2600";

	/* XP 64-bit SP2 */
	private static final String UA_MINIDIR_5_2_3790 =
			"Microsoft-WebDAV-MiniRedir/5.2.3790";

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		// NOOP
	}

	@Override
	public void destroy() {
		// NOOP
	}

	/**
	 * Check for the broken MS WebDAV client and if detected issue a re-direct
	 * that hopefully will cause the non-broken client to be used.
	 */
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
	                     FilterChain chain) throws IOException, ServletException {
		if (!(request instanceof HttpServletRequest) ||
				!(response instanceof HttpServletResponse)) {
			chain.doFilter(request, response);
			return;
		}
		HttpServletRequest httpRequest = ((HttpServletRequest) request);
		HttpServletResponse httpResponse = ((HttpServletResponse) response);
		String ua = httpRequest.getHeader("User-Agent");

		if (ua == null || ua.length() == 0 ||
				!ua.startsWith(UA_MINIDIR_START)) {
			// No UA or starts with non MS value
			// Hope everything just works...
			chain.doFilter(request, response);
		} else if (ua.startsWith(UA_MINIDIR_5_1_2600)) {
			// XP 32-bit SP3 - needs redirect with explicit port
			httpResponse.sendRedirect(buildRedirect(httpRequest));
		} else if (ua.startsWith(UA_MINIDIR_5_2_3790)) {
			// XP 64-bit SP2
			if (!"".equals(httpRequest.getContextPath())) {
				log(request,
						"XP-x64-SP2 clients only work with the root context");
			}
			// Namespace issue maybe
			// see http://greenbytes.de/tech/webdav/webdav-redirector-list.html
			log(request, "XP-x64-SP2 is known not to work with WebDAV Servlet");

			chain.doFilter(request, response);
		} else {
			// Don't know which MS client it is - try the redirect with an
			// explicit port in the hope that it moves the client to a different
			// WebDAV implementation that works
			httpResponse.sendRedirect(buildRedirect(httpRequest));
		}
	}

	private String buildRedirect(HttpServletRequest request) {
		StringBuilder location =
				new StringBuilder(request.getRequestURL().length());
		location.append(request.getScheme());
		location.append("://");
		location.append(request.getServerName());
		location.append(':');
		// If we include the port, even if it is 80, then MS clients will use
		// a WebDAV client that works rather than the MiniRedir that has
		// problems with BASIC authentication
		location.append(request.getServerPort());
		location.append(request.getRequestURI());
		return location.toString();
	}

	private void log(ServletRequest request, String msg) {
		StringBuilder builder = new StringBuilder(LOG_MESSAGE_PREAMBLE);
		builder.append(msg);
		request.getServletContext().log(builder.toString());
	}
}
